The conventional oil well lifting equipment of the oil field draws three-phase mixture of gas, oil and water during the downhole operation, and a small amount of which carry part of oil layer sand along with swabbing fluid. With lengthening of the development time of multiply formation field, water and sand contained in the swabbing fluid increase. If water content is too high during the production of oil well, the production cost will increase; if oil layer sand enters into the oil pump along with the fluid, the probability of stuck pump is greatly increased, which may result in unnecessary downhole servicing operation. Therefore, the prior separator used in the oil field can not effectively separate oil and water underground.